In the past, high lift farm dump boxes have been relatively unstable in their raised dumping position. This problem is present in the structures disclosed in a number of prior art patents, which are the closest prior art known to applicant at this time.
The basic problems that exist in the manufacture of high lift farm dump boxes are the necessity for a unit that will carry its full load when in lowered position in a stable manner, while providing the required ground clearance of at least 10 inches up to 24 or even 30 inches under certain conditions, while still permitting the necessary extensiblility to elevate the dump box above the upper edge of a transport truck or trailer unit into which the load is being dumped. This upper elevation requirement is accentuated when a guiding lip is added along the discharge edge of the dump box.
All of the prior art structures are limited in their extensibility by the fact that the bending moment produced by the elevated load derives its total support from the stationary hollow strut member and its relationship to the upper elevated member which is supported solely by its overlapped relation within the bottom stationary support member. This limits the amount of extension permitted to the length of the stationary base strut member minus the required overlap between the base member and the single extensible member. In order to permit extension of the upper extensible member beyond the upper end of the stationary base strut member, it is necessary to provide a rigid connection between the upper extensible member and the extensible intermediate member so that when the upper member and intermediate member are in fully extended position they will be rigidly connected and will operate as a single unit.
It is also necessary to provide maximum dumping efficiency that the box dumping cylinders operate in a substantially vertical position and that they be mounted on an intermediate portion of the extended strut assembly. This is accomplished by providing an intermediate cross bar assembly connected to the upper strut section and having its ends extending laterally outwardly beyond the sides of the dump box. The intermediate cross bar provides a rigid interlocked connection between the lower ends of the extensible strut members and the upper ends of the intermediate strut members so that the two extended strut sections provide a rigid unit which produces the necessary stability when the dump box is in raised position.
The following is a list of the patents which are familiar to applicant herein, copies of which are enclosed herewith.
______________________________________ PRIOR ART U.S. Pat. No. Issue Date Patentee ______________________________________ 2,105,329 January 11, 1938 Orlowsky 2,234,599 March 11, 1941 Johnston 2,286,416 June 16, 1942 Holmstrom 2,675,247 April 13, 1954 Meng 2,812,210 November 5, 1957 Osborn 3,083,058 March 26, 1963 Walstrom et al. 3,205,011 September 7, 1965 Diem 3,228,727 January 11, 1966 Paulson 3,362,085 January 9, 1968 Clifford et al. 3,633,971 January 11, 1972 Berky 3,712,675 January 23, 1973 Schoenwald 3,844,617 October 29, 1974 Kostman ______________________________________
None of the above patents shows the stabilizing interlocking cross bar construction disclosed herein.